ES2725443T3 - Method to prepare a system for maintenance - Google Patents

Abstract

Method for preparing a system (100) for a maintenance operation, said system (100) comprises - a first subsystem (110) containing a superatmospheric gas, - a second subsystem (120), and - a third subsystem (130) between the first subsystem (110) and the second subsystem (120); said first subsystem (110) and said second subsystem (120) are connected through an intermediate subsystem (170a), so that said intermediate subsystem (170a) - is capable of allowing gas to flow between the first subsystem (110) and the second subsystem (120) through the third subsystem (130), and - is located between the first subsystem (110) and the second subsystem (130); said intermediate subsystem (170a) comprises - a first sealant valve seat (231), - a second valve seat (241) between the first sealant valve seat (231) and the second subsystem (120); and - an air purge opening (246) between the first sealant valve seat (231) and the second valve seat (241); said third subsystem (130) and said second subsystem (120) are connected through another intermediate subsystem (170b) capable of allowing gas to flow between the third subsystem (130) and the second subsystem; said other intermediate subsystem (170b) comprises - a third sealant valve seat (231), - a fourth valve seat between the third sealant valve seat (231) and the third subsystem (130); and - a second air purge opening (246) between the third sealing valve seat (231) and the fourth valve seat (241); said method comprises - the discharge of gas present between the first sealant valve seat (231) and the second valve seat (241) through the air purge opening (246) before performing a step of the maintenance operation downstream of said second valve seat (241) with respect to the first sealant valve seat (231), and - the gas discharge present between the third sealant valve seat (231) and the fourth valve seat (241) a through the second air purge opening (246) before performing a maintenance operation step between the second valve seat (241) and the fourth valve seat (241); characterized in that the method, before performing a step of the maintenance operation with the intermediate subsystem (170a) and the other intermediate subsystem (170b) in a closed position, comprises - applying suction to the air purge opening (246) to discharge the gas present between the first sealant valve seat (231) and the second valve seat (241) before performing said maintenance step - the gas discharge present between the third sealant valve seat (231) and the fourth seat valve (241) through the second air purge opening (246) between the second valve seat (241) and the fourth valve seat (241) by applying suction to the second air purge opening (246); so that the suction is applied to achieve subatmospheric pressure, at least, in an intermediate system (170a, 170b) of the system (100).

Description

DESCRIPTION

Method to prepare a system for maintenance

[0001] The present invention relates to a method for preparing a system for a maintenance operation, said system comprises

- a first subsystem containing a superatmospheric gas,

- a second subsystem, and

- a third subsystem between the first subsystem and the second subsystem;

said first subsystem and said second subsystem are connected through an intermediate subsystem, so that said intermediate subsystem

- is capable of allowing gas to flow between the first subsystem and the second subsystem through the third subsystem, and

- is located between the first subsystem and the second subsystem;

said intermediate subsystem comprises

- a first sealant valve seat,

- a second valve seat between the first sealing valve seat and the second subsystem; Y

- an air purge opening between the first sealing valve seat and the second valve seat;

said third subsystem and said second subsystem are connected through another intermediate subsystem capable of allowing gas to flow between the third subsystem and the second subsystem; the mentioned other intermediate subsystem comprises

- a third sealant valve seat,

- a fourth valve seat between the third sealing valve seat and the third subsystem; Y

- a second air purge opening between the third sealing valve seat and the fourth valve seat;

said method comprises

- the gas discharge present between the first sealant valve seat and the second valve seat through the air purge opening before performing a maintenance operation step downstream of said second valve seat with respect to the first sealant valve seat, and

- the gas discharge present between the first sealing valve seat and the fourth valve seat through the air purge opening before performing a maintenance operation step between the second valve seat and the fourth valve seat .

[0002] Systems comprising superatmospheric gas are well known in the art. They are, for example, systems comprising natural gas, synthesis gas or carbon dioxide, in which the air is treated, or its pressure is increased or reduced. Said gas may be flammable, toxic, or constitute a hazard of some other type. It is often essential that a plant comprising such a system remains operational despite maintenance, or that maintenance downtime is kept to a minimum. However, the presence of gas escaped from the system at the place where maintenance should be performed may constitute a danger to the persons performing the maintenance. Depending on the work in question, they may be listed specialists, and their number be considerable. If the measurements of ambient gas at the place where maintenance is to be performed show that the gas leakage levels are above acceptable or acceptable according to safety procedures, the resulting delay may cost too much. To prevent gas from passing through the intermediate system to the atmosphere (environment) in the place where the maintenance operation is to be performed, it is known to block the gas so that it does not pass from the first subsystem to the immediate subsystem, using the first sealant valve seat , and then purge the gas from the intermediate subsystem into the outside atmosphere through an air purge opening.

[0003] The article "EMERGENCY PIPELINE REPAIR SYSTEMS DEVELOPED TO FACILITATE PIPELINE REPAIR OF UNPIGGABLE DEFECTS" / papers / 12-Aberdeen / 2012-07-STATS- Group-paper.pdf) discloses a method to prepare a system for gas discharge maintenance.

[0004] The object of the present invention is to provide a method with a reduced risk of delay and / or an increased level of safety and / or improve the availability of a plant or a large portion thereof. This, in particular, in the case of valve seat joints leaking or potentially leaking.

[0005] To this end, a method according to the preamble is characterized in that the method, before performing a step of the maintenance operation with the intermediate subsystem and the other intermediate subsystem in a closed position, comprises

- apply suction to the air purge opening to discharge the gas present between the first sealant valve seat and the second valve seat before performing said maintenance step;

- the gas discharge present between the third sealant valve seat and the fourth valve seat through the second air purge opening between the second valve seat and the fourth valve seat by applying suction to the second air purge opening air;

so that suction is applied to achieve subatmospheric pressure, at least, in an intermediate system of the system.

[0006] By applying suction to both the first air purge opening and the second, the risk that the gas present in the first subsystem can pass through the second valve seat and reach the place where it is reached is effectively reduced Maintenance should be performed. This can occur if the first sealant valve seat and the second valve seat do not seal properly. Thus, according to the invention, the third subsystem can be isolated from the first and second subsystems and subjected to maintenance without depressurizing neither the first subsystem nor the second.

[0007] In this patent application, maintenance includes any work on a third subsystem, be it inspection, cleaning, repair, modification or replacement of a part. A maintenance operation is a series of one or more maintenance steps, and the method according to the invention specifies that, at a minimum, one of them is not performed before the gas discharge using suction. The third subsystem typically comprises an apparatus such as a compressor, a flow measurement system, a gas drying equipment, a tank or container, a filter separator, a heat exchanger, a wellhead or a steam recovery unit .

[0008] The intermediate subsystems comprise, for example, a spherical valve, it comprises the valve seats and the air purge opening.

[0009] The active discharge (suction) of gas is achieved by a vacuum pump.

[0010] By way of example, a subatmospheric pressure between the first sealing valve seat and the second valve seat prevents gas from flowing further into the second subsystem. Any subatmospheric pressure is effective, no matter how tiny. For practical purposes, the subatmospheric pressure is at least 0.02 bar below the ambient atmospheric pressure, preferably at least 0.05 bar and more preferably at least 0.08 bar. A lower subatmospheric pressure makes the method less susceptible to any change of applied subatmospheric pressure or other disturbances.

[0011] It is preferable that both intermediate subsystems are at subatmospheric pressure.

[0012] In the present application, the concept of gas also includes steam. The concept of "sealing valve seat" is a seat to block the flow of pressurized gas from a pressurized subsystem to a subsystem at a lower pressure, such as a depressurized system.

[0013] Preferably, the gas is discharged using a purge conduit that releases the gas from the intermediate subsystem into the outside atmosphere in a safe place, away from the place where maintenance is to be performed. The purge line comprises, between a pressure gauge and a vacuum pump, a valve, eg an on / off valve, a control valve, a pressure regulator or a non-return valve.

[0014] WO2005 / 026603 discloses a method for purging gas by vacuum in a pipe or tank.

[0015] According to a favorable embodiment, the intermediate subsystem, the third subsystem and the other intermediate subsystem define a branch connecting the first subsystem with the second subsystem, in addition the system comprises a second branch connecting the first subsystem and to the second subsystem.

[0016] Such a system allows maintenance of the third subsystem of one branch, while the other branch remains operational, although it is possible that the system operates at a lower capacity.

[0017] According to a favorable embodiment, the system comprises a pressure gauge for measuring the pressure of an intermediate subsystem of the system.

[0018] This gives an indication of the safety of the area where maintenance is to be performed. The pressure gauge can also be used to control the vacuum pump used to provide suction. The pressure gauge can also be used in combination with a PLC to detect a sudden leakage rate (exceeding the preset pressure gradient limit) or a leakage rate that exceeds the capacity of the suction system (exceeding the preset pressure limit) and, in the event of a potentially dangerous situation, can be used to trigger an alarm without delay in the place where maintenance is performed and / or in the control room.

[0019] According to a favorable embodiment, the system comprises a pressure gauge for measuring the upstream pressure of a vacuum pump that provides said suction, so that the flow resistance Rvv-pg between i) the location of the gas between the first sealant valve seat and the second valve seat and ii) the location of the pressure gauge is less than the flow resistance Rpg-vp between i) the location of the pressure gauge and ii) the vacuum pump.

[0020] Thus, the risk that, in case of a strong leak in the first sealing valve seat, the pressure measured by the pressure gauge represents the pressure between the first sealing valve seat and the second valve seat, can be reduced a subatmospheric reading indicating that no gas will pass from the first subsystem to the second valve seat. The relatively high flow resistance between the pressure gauge and the vacuum pump can be achieved using throttling. For practical purposes, the throttling is balanced with the expectation of effectively extracting gas to be discharged by the vacuum pump.

[0021] According to a favorable embodiment, the gas extracted by suction is diluted to reduce its Lower Explosive Limit.

[0022] For example, natural gas is diluted below 5% by volume of natural gas in the air. Thus, it cannot explode.

[0023] According to a favorable embodiment, the dilution is carried out with an inert gas.

[0024] The inert gas is, for example, carbon dioxide. According to an interesting embodiment, the inert gas is exhaust gas obtained by combustion, eg consuming a hydrocarbon such as methane, propane, butane, or a liquid fuel such as gasoline or diesel. In this way it is possible to reduce the oxygen content of the air before dilution. This significantly saves the amount of gas used to dilute. Advantageously, the inert gas is nitrogen or steam, either being available in plants.

[0025] According to a favorable embodiment, the suction is applied using a Venturi vacuum pump.

[0026] Thus, the gas extracted from the intermediate system does not pass through any part with mechanical movement that could cause ignition if the gas were flammable. The Venturi type pump is an ejector or jet pump. If the extracted gas is flammable, the Venturi pump is preferably fed with an inert gas such as nitrogen or steam instead of air, reducing the risk of an explosive atmosphere in the medium used to discharge the gas.

[0027] According to a favorable embodiment, the intermediate subsystems comprise a spherical valve, said spherical valve comprises the first sealing valve seat, the second valve seat and the air purge opening.

[0028] Spherical purge valves are an important area of application of the method according to the invention.

[0029] According to a favorable embodiment, the second valve seat is a second sealant valve seat.

[0030] In this case it is easier to achieve subatmospheric pressure. In addition, the second sealant valve seat acts as a safety measure if there is a failure in the system, which achieves a subatmospheric pressure. A spherical valve comprising a first and second sealant valve seats is commercially available as a spherical valve with double piston effect, that is, as a double lock and bleed valve.

[0031] According to a favorable embodiment, the fourth valve seat is a fourth sealant valve seat.

[0032] In this case it is easier to achieve subatmospheric pressure.

[0033] According to a favorable embodiment, the subatmospheric pressure is maintained while at least one step of the maintenance operation is performed.

[0034] So, the method is to perform maintenance. Preferably, the subatmospheric pressure is preserved throughout the maintenance process, thus reducing the risk of gas leaks during the entire maintenance procedure through an intermediate system to the third depressurized subsystem.

[0035] According to a favorable embodiment, the pressure in the intermediate subsystem is monitored using a pressure gauge, and a vacuum pump used to apply suction is controlled with the pressure gauge.

[0036] This saves energy and / or, if an inert gas such as nitrogen is used (eg when using a motor gas), saving inert gas. This suction control is achieved, for example, by controlling the flow of the engine gas for a Venturi vacuum pump.

[0037] According to a favorable embodiment, the purge line comprises a non-return valve between the pressure gauge and the vacuum pump.

[0038] When a sufficiently low pressure is achieved in the intermediate subsystem, by measuring with the pressure gauge, the vacuum pump can be stopped, whereby the non-return valve closes. If then the pressure in the intermediate subsystem increases due to leaks of pressurized gas and / or air in the intermediate subsystem, and exceeds a certain preset level, the vacuum pump can be restarted, until the pressure is low enough to stop the pump again, etc. If there are few leaks of air and / or pressurized gas to the intermediate system, only a limited operating time needs to be applied to the pump, achieving significant energy and / or inert gas savings.

[0039] According to a favorable embodiment, the third subsystem comprises a compressor.

[0040] Thus, more specifically, the method according to the invention refers to a method for preparing a system comprising a compressor, which is an important area of application of the method.

[0041] Next, the present invention will be illustrated with reference to the illustrations, wherein

fig. 1 shows a schematic arrangement of a subatmospheric pressure system;

fig. 2 shows a sectional view through an intermediate subsystem of the system of fig. one; and fig. 3 shows a schematic arrangement of a superatmospheric pressure system similar to fig. one.

[0042] Fig. 1 shows a schematic arrangement of a system 100 comprising a first subsystem 110 and a second subsystem 120. The system 100 comprises a first branch 101 connecting the first subsystem 110 with the second subsystem 120; and comprises a second branch 102 that also connects the first subsystem 110 with the second subsystem 120.

[0043] In one embodiment discussed here, the natural gas in the first subsystem 110 with a pressure of 90 bar sees its pressure raised to 200 bar with compressors 121, 121 '. If the compressor 121 of the first branch 101 needs maintenance, it needs to be isolated from any subsystem that remains pressurized and brought to atmospheric pressure. To this end, there is an intermediate subsystem 170a between the first subsystem 110 and a third subsystem 130 comprising the compressor 121; and another intermediate subsystem 170b between the third subsystem 130 and the second subsystem 120. The intermediate subsystem of the first branch comprises a spherical valve 123 upstream, and the other intermediate subsystem 170b comprises a spherical valve 122 downstream. To perform maintenance on the compressor 121, both ball valves are closed. Conveniently, said spherical valves are double piston effect valves.

[0044] The internal volume of the ball valves contains high pressure gas. As is known in the type, this gas is discharged into the (outer) atmosphere through a purge opening.

[0045] If, for example, the upstream ball valve 123 leaks, the gas may continue to leak from the first subsystem 110 to the compressor 121, causing a dangerous situation.

[0046] According to the present invention, a subatmospheric pressure is applied to the spherical valves by connecting a purge line 150 and a vacuum pump 160 to the purge opening. This will be discussed in greater detail with reference to fig. 2.

[0047] To apply the subatmospheric pressure, the purge line 150 is provided with an ejector vacuum pump 160, driven by an air pump 161. This air pump 161 preferably provides as much engine air as the gas in the line. Purge 150 is diluted to reduce the Lower Explosive Limit, eliminating the danger of an explosion, and is discharged through a section of purge line 150 downstream of ejector vacuum pump 160 to a safe place.

[0048] By keeping the valves 122 ', 123' of the second branch 102 open, the second branch 102 can remain operative and, meanwhile, maintenance can be performed on the first branch 101.

[0049] Fig. 2 shows a sectional view through an intermediate subsystem 170 of the system of fig. 1, embodied in a spherical valve comprising a housing 205. The spherical valve is a standard spherical valve with double piston effect, comprising a first sealant valve seat 231 and a second seat of sealing valve 241. The valve seats can slide into the corresponding seat cavities. In general there will be o-rings (not shown) to seal the valve seats against the seat cavities. The first sealing valve seat 231 comprises a through hole 232 and the second sealing valve seat 241 comprises a through hole 242.

[0050] In addition, the ball valve comprises a sphere 233 with a through hole 234. Springs 291 are present to push the valve seats against the ball 233. The ball 233 can be rotated by means of spindle 292 to open and close the ball valve. In fig. 2 is closed. If the sphere 233 is rotated 90 °, the through holes 232, 234 and 242 are aligned and the sphere 233 allows the gas to pass through the ball valve.

[0051] To discharge gas present in the cavity 245 of the ball valve a purge opening 246 is provided, which is connected to the purge line 150.

[0052] A spherical valve like the one disclosed is already known in its type.

[0053] In accordance with the present invention, suction is applied. Thus, not only is gas actively discharged from cavity 245, but, more importantly, gas leaks are reduced by the first sealant valve seat 231 through the second valve seat 241 and, if subatmospheric pressure is achieved in The spherical valve cavity, are prevented. In this way, the escape of gas from the first subsystem 110 downstream of the second valve seat 241 can be prevented, helping to create a safe working environment for performing a maintenance operation.

[0054] In the embodiment shown there is a pressure gauge 270 to determine if subatmospheric pressure has been achieved, indicating that no gas will escape from the ball valve. The pressure gauge 270 can be used to control the air pump 161, which can save energy and / or save inert gas such as nitrogen, if it is used as the engine gas. In the embodiment shown in fig. 2, the purge line 150 between the manometer 270 and the vacuum pump 160 comprises a non-return valve 287. When a sufficiently low pressure is achieved in the intermediate subsystem, measured with the manometer, the vacuum pump can be stopped, thereby that the check valve closes. If then the pressure in the intermediate subsystem increases due to leaks of pressurized gas and / or air in the intermediate subsystem, and exceeds a certain preset level, the vacuum pump can be restarted, until the pressure is low enough to stop the pump again, etc. If there are few leaks of air and / or pressurized gas to the intermediate system, only a limited operating time needs to be applied to the pump, achieving significant energy and / or inert gas savings.

[0055] The purge line 150 contains a throttle 251. As a result, the flow resistance in an upstream section 252 of the purge line 150 where the pressure gauge 270 is located is less than the flow resistance in a current section below 253 between the pressure gauge 270 and the ejector vacuum pump 160. Thus, the reliability of the pressure gauge 270 being able to indicate that a subatmospheric pressure is present in the cavity 245 is increased when the pump is in operation and the check valve 287 it's open.

[0056] An air purge opening 293 may be present between the first sealing valve seat 231 and the second valve seat 241) During normal operation, this air purge opening 293 is closed with a plug. While it is not preferred because gas could escape through it, an air purge opening 293 is permissible if strong suction is applied with the vacuum pump (here, ejector vacuum pump 160), in particular if the flow resistance to through said air purge opening 293 is greater than the resistance of the flow in the purge line 150 from the cavity to the ejector vacuum pump 160. Thus, ambient air is sucked in, preventing the gas from escaping from the cavity 245 through the air purge opening 293.

[0057] The air purge opening 293 may be advantageously provided with the manometer 270, to ensure that the manometer reading corresponds to the pressure in the cavity and is not affected by any loss of dynamic pressure in the line of purge 150.

[0058] Fig. 3 corresponds substantially to fig. 1, with the difference that instead of spherical valves (with double piston effect) two pairs of single sealant seat valves 330 are used. Each pair has a purge line 336 provided between the two single sealant sealant valves 330 of that pair

[0059] By closing said simple sealant seat valves 330, and opening the valves 335 of the purge lines 336, suction can be applied and the gas present between the single sealant seat valves 330 of each pair is discharged.

[0060] When for the second branch 102, which connects the first pressurized subsystem 110 with the pressurized subsystem 120, the valves 330 are kept open and the valves 335 are kept closed, the second branch 102 can remain operative, so that perform maintenance on the first branch 101 safely.

[0061] The method according to the present invention may vary in various ways within the scope of the claims attached. For example, if one of the pressurized subsystems 110, 120 is depressurized during maintenance, only an intermediate subsystem 170 is necessary. The purge lines 150 may be permanently present in a system, or connected to an intermediate system using a system of mobile vacuum before maintenance and remove after maintenance. Each individual intermediate subsystem can have an individual suction system, independent of other intermediate subsystems, or they can be combined in any favorable combination, depending on the situation in question.

Claims (14)

1. Method for preparing a system (100) for a maintenance operation, said system (100) comprises - a first subsystem (110) containing a super-thermospheric gas, - a second subsystem (120), and - a third subsystem (130) between the first subsystem (110) and the second subsystem (120); said first subsystem (110) and said second subsystem (120) are connected through an intermediate subsystem (170a), so that said intermediate subsystem (170a) - is capable of allowing the gas to flow between the first subsystem (110) and the second subsystem (120) through the third subsystem (130), and - is located between the first subsystem (110) and the second subsystem (130); said intermediate subsystem (170a) comprises - a first sealant valve seat (231), - a second valve seat (241) between the first sealant valve seat (231) and the second subsystem (120); Y - an air purge opening (246) between the first sealant valve seat (231) and the second valve seat (241); said third subsystem (130) and said second subsystem (120) are connected through another intermediate subsystem (170b) capable of allowing gas to flow between the third subsystem (130) and the second subsystem; said other intermediate subsystem (170b) comprises - a third sealant valve seat (231), - a fourth valve seat between the third sealing valve seat (231) and the third subsystem (130); and - a second air purge opening (246) between the third sealing valve seat (231) and the fourth valve seat (241); said method comprises - the discharge of gas present between the first sealing valve seat (231) and the second valve seat (241) through the air purge opening (246) before performing a step of the maintenance operation downstream of said second valve seat (241) with respect to the first sealant valve seat (231), and - the gas discharge present between the third sealant valve seat (231) and the fourth valve seat (241) through the second air purge opening (246) before performing a maintenance operation step between the second valve seat (241) and the fourth valve seat (241); characterized in that the method, before performing a step of the maintenance operation with the intermediate subsystem (170a) and the other intermediate subsystem (170b) in a closed position, comprises - apply suction to the air purge opening (246) to discharge the gas present between the first sealant valve seat (231) and the second valve seat (241) before performing said maintenance step - the gas discharge present between the third sealant valve seat (231) and the fourth valve seat (241) through the second air purge opening (246) between the second valve seat (241) and the fourth valve seat (241) applying suction to the second air purge opening (246); so that the suction is applied to achieve subatmospheric pressure, at least, in an intermediate system (170a, 170b) of the system (100). 2. Method according to claim 1, so that the intermediate subsystem (170a), the third subsystem (130) and the other intermediate subsystem (170b) define a branch (101) connecting the first subsystem (110) with the second subsystem (120), in addition the system (100) comprises a second branch (102) that connects to the first subsystem (110) and the second subsystem (120). 3. Method according to claim 1 or 2, so that the system (100) comprises a pressure gauge (270) for measuring the pressure of an intermediate subsystem (170a, 170b) of the system (100). Method according to claim 3, so that the system (100) comprises a pressure gauge (270) for measuring the pressure upstream of a vacuum pump (160) that provides said suction, so that the resistance of Rvv-pg flow between i) the location of the gas between the first sealing valve seat (231) and the second valve seat (241) and ii) the location of the pressure gauge (270) is less than the flow resistance Rpg-vp between i) the location of the pressure gauge (270) and ii) the vacuum pump (160). 5. Method according to any of the preceding claims, so that the gas extracted by suction is diluted to reduce its lower explosive limit. 6. Method according to claim 5, so that the dilution is carried out with an inert gas. 7. Method according to any of the preceding claims, so that the suction is applied using a Venturi vacuum pump (160). Method according to any of the preceding claims, so that the intermediate subsystems (170a, 170b) comprise a spherical valve (123), said spherical valve (123) comprises the first sealant valve seat (231), the second valve seat (241) and air purge opening (246). 9. Method according to any of the preceding claims, so that the second valve seat (241) is a second sealant valve seat (241). 10. Method according to any of the preceding claims, so that the fourth valve seat (241) is a fourth sealant valve seat (241). 11. Method according to any of the preceding claims, so that the subatmospheric pressure is maintained while at least one step of the maintenance operation is performed. 12. Method according to any of the preceding claims, so that the pressure in the intermediate subsystem (170a) is monitored using a pressure gauge (270), and a vacuum pump (160) used to apply suction is controlled with the pressure gauge (270). 13. Method according to claim 12, such that a purge line (150) between the pressure gauge (270) and the vacuum pump (160) comprises a non-return valve (287). 14. Method according to any of the preceding claims, so that said third subsystem (130) comprises a compressor (121).